This invention relates to valves and, more particularly, to the sealing of valves during closure.
Valves are used in many fields for controlling the flow of liquid and gaseous media and throughout this specification and claims, such media will be referred to simply as a fluid or fluids as the context requires.
Numerous forms of valve have been proposed having a valve seat member and a valve closure member movable towards and away from the seat member to close and open the valve to control fluid flow through the valve. In order to produce and maintain a satisfactory seal during closure, confronting surfaces of the seat and closure member must be fashioned in strict conformity. Such strict conformity requires, in many instances, accurate machining of the confronting surfaces of the members.
It is known to control the operation of valves by mechanical, electrical, electronic and pneumatic means.
Piezo electric control valves have also been proposed as substitutes for solenoid controlled valves and are preferable in installations where size and weight are important design considerations. Piezo electric control valves may take the form of discs, usually circular, and beams which may be supported at each end or simply, cantilevered.
Where piezo electric control valves are in the form of circular discs, peripheral flatness not infrequently introduces sealing problems. This is principally due to the fact that it is difficult to produce, on a production basis, relatively thin metal discs possessing a sufficiently high degree of flatness to mate with a corresponding flat surface machined or otherwise formed on a valve seat. Typically, such 30 thin metal discs constitute substrates for supporting piezo electric ceramic materials on one or each face of the disc. Examples of such piezo electric valves are described in U.S. Pat. Nos. 4,545,561 and 3,360,664, the disclosures of which are incorporated by reference herein.
In prior U.K. patent application no. 9122739.7 there is described and claimed a piezo valve for controlling fluid flow, the valve comprising a valve housing, a cavity within the housing, inlet and outlet ducts leading fluid into and out from the cavity, a movable piezo electric valve disc element, disposed in the cavity, and means for supporting the valve disc element at a position inwardly of the disc periphery so that upon actuation of the element by a voltage applied thereto, the periphery of the disc is displaceable and at least a portion of a peripheral region of the disc serves to control fluid flaw between the inlet and outlet ducts.
The peripheral flatness of a piezo electric disc forming part of a valve described in U.K. no. 9122739.7 is typically of the order of .+-.250 .mu.m whereas the opening per se for fluid flow is of the order of .ltoreq.300 .mu.m. It will therefore, be appreciated that if closure is achieved using a pliant sealing member to accommodate the tolerance mentioned, the effective valve opening could be reduced to 300-250 =50 .mu.m. Such an opening is generally insufficient to achieve a satisfactory flow fluid when the valve is open. In addition, the peripheral flatness problem also manifests itself when using a pliant seal in so far that the seal produces an unexpectedly adverse fluid flow against voltage characteristics.
It is an object of the present invention to provide a production system which will provide a relatively low cost valve seal for accommodating normal production tolerances without wasting operational movement of the valve.
According to one aspect of the present invention, a valve comprises a valve seat member and a movable valve member movable towards and away from the valve seat member to close and open the valve. A sealing element made from a resilient material is attached to one of the members (preferable the valve seat member). The sealing element possesses an initial deformable characteristic such that initial closure of the valve causes the sealing element to substantially conform to the shape of the other member (movable valve member) and retain the so-conformed shape. Preferably, the sealing element is permanently attached to the valve seat member.
The movable valve member is preferably in the form of a piezo electric disc comprising a substrate having a layer of piezo ceramic applied to at least one face thereof.
According to a further aspect of the present invention a method of forming a valve seat for creating a seal against a valve member having an irregular surface is provided. The method comprises the steps of: (a) assembling the valve seat from two compliant elements disposed in juxtaposition, each element initially possessing a different resiliently deformable characteristic, one having a least and the other a most resiliently deformable characteristic, and together constituting a seal assembly which conforms to the peripheral shape of the valve member. (b) placing the seal assembly in a housing with the element possessing the least resiliently deformable characteristic most remote from the movable valve member. (c) applying pressure to the seal assembly via the movable valve member so that the least resiliently deformable element absorbs the surface irregularity of the valve member without substantially changing the deformability characteristic of the other element, and, (b) maintaining the element possessing the least resiliently deformable characteristic in that attitude where the surface irregularity of the movable valve member is absorbed.
The compliant (resilient) elements may be made from any suitable synthetic or natural rubber-like material.
Thus, a material may be chosen to achieve the dichotomous properties in a single component which posses two mechanical states: the first being soft and compliant and the second being semi rigid with the required changes described above being easy to effect yet irreversible.